(Corrects penultimate paragraph to source quote to TV Asahi, not Asahi TV. This error also appeared in previous updates of this story)
* Dead man's passport in name of Kim Chol -Malaysian police
* Cause of death not yet known; reports of poisoning
* Two women fled airport by taxi after attack -South Korean TV
* Deceased fell ill at airport, died en route to hospital
By Emily Chow and Ju-min Park
KUALA LUMPUR/SEOUL, Feb 14 (Reuters) - The U.S. government strongly believes that North Korean agents murdered the estranged half-brother of North Korean leader Kim Jong Un in Malaysia, U.S. government sources said on Tuesday.
American authorities have not yet determined exactly how Kim Jong Nam was killed, according to two sources, who did not provide specific evidence to support the U.S. government's view.
A South Korean government source also had said that Kim Jong Nam had been murdered in Malaysia. He did not provide further details.
South Korea's foreign ministry said it could not confirm the reports, and the country's intelligence agency could not immediately be reached for comment.
In Washington, there was no immediate response to a request for comment from the Trump administration, which faces a stiff challenge from a defiant North Korea over its nuclear arms programme and the test of a ballistic missile last weekend.
Kim Jong Nam was known to spend a significant amount of his time outside North Korea and had spoken out publicly against his family's dynastic control of the isolated state.
If confirmed as an assassination, it would the latest in a string of killings over the decades at home and abroad meant to silence those perceived by North Korea's leaders as threats to their authority, one of the U.S. sources said on condition of anonymity.
In a statement, Malaysian police said the dead man, 46, held a passport under the name Kim Chol.
Kim Jong Nam has been caught in the past using forged travel documents.
Malaysian police official Fadzil Ahmat said the cause of Kim's death was not yet known, and that a post mortem would be carried out.
"So far there are no suspects, but we have started investigations and are looking at a few possibilities to get leads," Fadzil told Reuters.
According to Fadzil, Kim had been planning to travel to Macau on Monday when he fell ill at the low-cost terminal of Kuala Lumpur International Airport (KLIA).
"The deceased ... felt like someone grabbed or held his face from behind," Fadzil said. "He felt dizzy, so he asked for help at the ... counter of KLIA."
Kim was taken to an airport clinic where he still felt unwell, and it was decided to take him to hospital. He died in the ambulance on the way to Putrajaya Hospital, Fadzil added.